Variable pitch airscrews



` July 12, 1960 T'. E. .GOUDEN ETAL 2,944,769

VARIABLE FITCH AIRSCREWS Filed Jan. :5, 1955 y 4 Sheets-Sheet l Ik?! i July 12, 1960 T. E. GoDDEN ETAL i A2,944,769

VARIABLE FITCH AIRSCREWS Filed Jan. 3, 1955 l 4 Sheets-Shea?l 2 'b m o f Q EN l l l J i Q .v

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O Q C) July-l2, 1960 v T. E. GODDEN ETAL 2,944,769

' VARIABLE FITCH AIRscREwsl Filed Jan. s, 1955 4 sheets-sheet s July 12, 1960 T. E.`GoDDEN ET AL 2,944,769

l VARIABLE FITCH AIRscREws Filed Jan. s, 1955 4 sheets-sheet 4 2,944,169 VARIABLE PITCH AIRSCREWS Thomas Edward Godden and Edward Hollingworth Morris, Gloucester, England, assignors vto Rotol Limited,

Gloucester, England, a British company 1 Fired Jari. 3, 1955, ser. No, :419,576 Y Claims priority, application Great Britain Dec. 30, 1954 7 claims. (ci. 244-81) This invention concerns hydraulic variable pitch propellers for aircraft of the kind in which movement of the blades of the propeller in the ne pitch direction is no1',- mally limited by a mechanicalne pitch stop which is retractable by hydraulic means.

Such a stop comes into action to prevent undesired iining oif of the pitch of'a propeller controlled by a constant speed device when the engine of an aircraft is throttled back prior to touch down on landing.V Should some fault have occurredin the hydraulic system or in the mechanism of the stop itself, causing the stop not' to be operative in the conditions referred to above, `the excessive ning off of the pitch will cause an unexpected increase in drag and may cause the aircraft to crash, or at least to lmakeaheavy landing.`V Y

a Duplication of the ne pitch stop and all its control system as, a means of safeguarding-against this. danger is impracticable on the ground of complication and the object of this invention is to provide a simple 'alternative arrangement which Vwill be applicablel both to thatkind of hydraulic variablepitch propeller. in'v which the tine pitch stop Vmechanism is retracted by a temporary increase 't the supply of hydraulic fluid to the pitch-changemecha-V ice' l ditions under which the ne pitch stop should be in its operative position one or more `electric switches arranged to be operated by the propeller on reaching said nner pitch setting, and electrically controllable means in circuit with said switches for eifecting temporary displacement in the pitch-coarsening sense of a valve controlling nism of the propeller.

A common requirement is that the tine pitch stop.

should normally be retractable only while the aircraft is e not airborne, andnin this case, according to a feature of in the pressure of fluid supplied to the propeller to oper- Accordin to the invention a h draulic variable itch t h g y p e ing orthe pitch ning sides of said motor, a fine pitch coarsening initiating means t-o initiateV coarsening of the pitch of the propeller which coarsening initiating means is operated by means detecting conditions under .which said stop should be in its operative position when such conditions exist and by the propeller on reaching apitch setting which is a predetermined amount iiner than that corresponding to the limit set by said stop, the propeller and the detecting means acting together to operate the coarsening initiating means. v

According to a feature Vof the invention, said pitch coarsening initiating means actY to produce Va temporary pitch-coarsening impulse in the hydraulic pitch-change mechanism of the propeller each time the pitch decreases to said ner setting, so that the average pitch setting is coarser than said nner setting. andpreferably approximates to the pitch setting as determined by normal operation of said fine pitch stop.V

the invention said coarsening initiatingA means may include one or more electric switches operated by relative Ymovement of undercarriage parts of the aircraft so as to render said coarsening initiating means inoperative as the undercarriage deects under the Weight of the aircraft. The invention also includes a particular construction of propeller comprising a double-acting hydraulic pitch change motor, a reciprocable Valve to control the admission of fluid under pressure alternatively to the pitch coarsening or the pitch-iining sides of said motor,'a fine pitch 'stop maintained in operative position'by a spring acting in opposition to a piston loaded by pressure uid in communication with the pitch iining side of said motor, pressure relief means Varranged to prevent rise of said pitch tlning pressure to arvalueV suiiicient to overcome said spring, means for loading said pressure relief means to allow said pitch iining pressureto rise to a valuesutlicient to overcome said spring, an electrical switch operated-by displacement of the propeller pitch-change mechanisrn in the pitch ning direction beyond said ne pitch stop, an electrical switch operated by means detecting when said ne pitch stop should be in its operative position and electrical means controlled by the combined operationtorf said switches to cause or initiate an impulse upon said reciprocable valve in the sense to increase the admission of fluidto the pitch coarsening vside of said motor.

'The invention also includes a further particular construction of propeller comprising a double-acting hydraulic pitch change motor, a reciprocable valve to control the admission of fluid alternatively to the pitch coarsenstop maintained in operative position by a spring acting inV opposition toV a piston, means for supplying fluid under pressure through a supply line separate from the' supply lines which supply iluid to and from the motor, to release said line pitch stop for retraction, an electrical Switch operated by displacement of the propeller pitch-change mechanism in the pitch iining direction beyond lsaid tine pitch stop, an electrical switch operated by means detectingy when said fine pitch stop should be in its operative position and electrical means controlled Y by the combined operation of said switches to cause or initiate an impulse upon said reciprocable valve inthe sense to increase the admission'of Huid to the pitch coarsening side of said motor.

Preferably, in a propeller as dened in the last pre- Aceding paragraph the means for supplying fluid to acti ,upon said pistonV comprises a conduit separate from coni Y duits through which fluid flows to the pitch-coarsening According to a further feature of the invention said f meansv initiating coarsening ofthe pitch of thelpropeller do so by causing the temporary Ydisplacement of a Valve controlling the supply of hydraulic uid to the pitchchange mechanism of the propeller into a position allowing a substantial ow of fluid to take place in the sense t to cause coarsening of the pitch of the propeller.

According to yet another feature of the invention said means initiating coarsening of the pitch include one or more electric switches operative by means detectingY conln the drawings:

Figure 1 illustrates the hub construction of the propeller;

.Figure 2 is a section along line 2-2 in Figure l;

.Figure 3 shows the relevant parts of the hydraulic circuit associated with the propeller, and

Figure 4 shows the relevant parts of the electrical circuits associated with the propeller and the undercarriage of an aircraft in which the propeller is mounted.

Referring to Figure l the propeller comprises a hub 11 upon which are journalled a number of blades, of which the root 12 of one only is shown, for rotation about their longitudinal pitch change axes. Each blade root 12 is provided with a crank pin, the axis of one of which is shown at 13, coupled by a connecting rod 14 to a ram 15 slidable in a cylinder 16 arranged coaxially with a driving shaft 17 on the nose portion of the hub 11. The ram 15 and cylinder 16 form two elements of a pitch change motor relative movement between which brings about pitch change adjustment of the propeller. The ram is of annular form and is slidable upon a stationary barrel 13 which houses retractable tine pitch stop mechanism. The ne pitch stops are in the form of abutments 1i? which are mounted on resilient fingers Ztl. Inward movement of the abutment 19 is controlled by a retaining ring 21, having two diameters 21a and 2lb on a stepped annular stop-release piston 22 sliding within a second barrel 23 forward of the abutments 19 and coaxial with the barrel 18, which barrel 23 is integral with, and closed at its forward end by, the nose cap 24 of the cylinder 16. The piston 22 is also slidable upon a central cylindrical part 25 and is normally held at the forward end of its stroke by a coil spring 26 and isA movable rearwardly against the pressure of this spring under a sufficiently elevated differential pressure applied thereto as will be described hereinafter, thereby to bring the smaller diameter part 2lb of the retaining ring 211 under the abutments 19 so that these latter can move inwardly to permit further forward movement of the ram 15. The ram is provided with a sleeve 27 which is a sliding fit on the barrel 18, its forward end being provided with a chamfered abutment 28. Projecting forward from this sleeve 27 is an annular ring 29 the forward end of which is also provided with a charnfered abutment 30. The internal diameter of this ring is such that the chamfered abutment 30 will engage the abutments 19 when these are held in their outer positions by the surface 21a of the retaining ring 21 but will slide over these abutments when the piston 22 is moved rearwardly to bring the surface 2lb under the abutments. Forward movement of the ram 15 is then limited by the abutment 28 engaging the abutments 19 which are moved forward to abut on the rearward face of the barrel 23.

A channel 31 concentric with the driving shaft 17 passes through the centre thereof into the propeller hub. This channel is used to convey coarse pitch pressure fluid to the forward side of the ram 15 of the pitch change motor via a chamber 32, ports 33, chamber 34, ports 35. annular chamber 36 surrounding the central cylindrical part 25 and through the clearance between the individual abutments 19 to move the ram 15 in the pitch-coarsening direction.

Surrounding channel 31 is an annular channel 37 which is used to convey iine pitch pressure iluid to the rearward side of the ram 15 via ports 33, channel 39, annular chamber dit and ports 41 to move the ram in the pitch-fitting direction.

A third channel d2, hereinafter referred to as the third oilway surrounds channel 37 and is used to convey hydraulic liuid from a source which will be later described, via channels i5 and 4d, annular chamber d5, ports 46 and 47, annular chamber 48, ports 49 and 50 to the forward side of the annular stop-release piston 22.

Mounted at vthe root end of each blade as shown is a cam 51 which, when the propeller blades moveto a predetermined angle e.g. two degrees below the ne pitch stop position, in which abutments `-19 and 30 are in engagement, engages a lever 52 pivoted at 53 to the hub 11. An abutment 52a on the lever bears against the plunger 54 of an electrical switch arrangement'shown generally at 55 (comprising a propeller switch means) which cooperates with a pair of coaxial electrical slip rings 56 and 57 mounted in a ring 58 of suitable material which electrically insulates them from one another and which is supported on the forward end of the engine adjacent the propeller. Both Vslip rings and insulating ring are coaxial with respect to the driving shaft 17. The plunger 54 which is housed in a bore 59 is provided with a stein which extends into the bore 61 of a sliding member 62 which carries a brush' 63. This brush is pivotall'" -2 mounted at the rearward extremity of this member by means of a pin 64, and is provided with a slot so that the two projections 65a and 65h formed on either side thereof align with the slip rings 56 and 57. The bore 59 is reduced in diameter at 59a to form a shoulder between which and the underside of the plunger 54 a coil spring 54a is interposed. A second but weaker coil spring 5111 is interposed between the underside of the plunger and a shoulder 62a on the sliding member 62. The bore of the sliding member at its forward extremity is reduced 1n diameter at 62b, the stem of the plunger being a sliding tit therethrough.Y The stern is provided at its rearward end with washers 60a conveniently secured thereto which are a sliding fit in the main bore 61 of the sliding member. It will be understood that the brush 65 is adequately insulated in any convenient manner from the sliding member.

Referring now to Figure 3 which is diagrammatical only, a constant speed unit'generally indicated 'at 66 comprises a casingr67 which at its lower end 68 houses a valve 69 provided with lands 70 and 71 and a bore 72. leading from a chamber 74 below said valve' intoan annular space surrounding it 'above the land 70. The valve extends upwardly and is provided with a shoulder 75 against the undersiderof which bear the inner endsrof governor ilyweights 76'which arepivotally mounted at '77 in a manner not shown, such that they are rotatable by a drive from the engine (not shown). in a practical construction the iiyweights are carried by the upper end of a ported sleeve interposed between the valve 69 and the casing 68, the sleeve being rotated by a drive shaft from the engine.

Above the shoulder 75, the valve 69 is reduced in diameter Iand at its upper end is provided with a further shoulder 78. The casing 67 is, in the vicinity of the flyweights '76, increased in size (79) but above the fly- Weghts is reduced again at 80 to provide a bore 817Goaxial withk the valve 69. This bore houses a sliding cylindrical member 82 provided with an inwardly directed shoulder 33 at its lower extremity and on one side with a gear rack S4. An aperture is provided in the vicinity o-f 4this rack in the wall of the casing 89 to permit a gear wheel 85 to mesh with said rack. Gear wheel 85 is mounted on a shaft (not shown) controlled by fthe pilot as hereinafter described. A coil spring 56 is interposed between the shoulders 75 and S3. Slidingly mounted in the bore of the cylindrical member 82 is a stepped "cylindrical member87, the lower extremity of which is provided with an inwardly directed 'shoulder 83. The arrangement is such that the upper end of the valve 69 is entered into said member v87 the shoulder 78 being disposed above the shoulder 88 and since shoulder 78 is larger in diameter than the Yhole surrounded by shoulder 8S, the valve 69 and stepped cylindrical member 87 are coupled with a certain amount of lost linear motion between them. The stepped cylindrical member S7 is reduced in diameter `at 89 and this part carries a stepped piston '90 secured thereto.` On either side of this piston the walls of the casing lincorporate inwardly Vdirected flanges 91 and '92 which form theV ends of a cylinder in which "the vpiston is operable against the casing 80, may engage. This lever is mechanicallyl con-rA nected to the fuel isolating valve of the engine and acts as a two-position stop for the member 89 i.e. for the feathering and constant speeding positions of this mem-l ber.

A conduit 96 for the passage of pressure fluid fromY the engine driving theV propeller leads to. the, constant speed unit pump 97 which is driven by the engine through the same transmission (not shown) which drives the governor assembly. lA non-return Yvalve. 98 is provided wffeiifthe fluid delivery line 99 from the pump. A line v1 00 /9 is taken from the line 99 downstream of the non-return valve to a pressure relief valve 101 which connects through theline 102 back to the conduit 96. Line 99 leads to a port 103 in the wall of the casing 68 communicating with the annular space between lands-70 and 711 of the valve 69. A line 104 is taken from line 99 to'a solenoid valve unit 105 and a line 10.6 branches from line 104 to a solenoid valve unit 107. A further line 108 is taken from line 106 to a iiuid pressure operated valve 109. Solenoid valve unit 105 comprises ahollowcasing trical solenoid 111. The valve member 112 is provided with upper and lower conical parts ,113 and 114 at either valve is closed under pressure of a spring 110e and the lower partrclosing onto a seating 116 when it is opened in the wall of the upper part of the Vcasing 110 opens into a line 118 which lcadsthrough a port 80a inthe Solenoid valve unit' 107 also' comprises a hollowicasf ing 119 the lower half of whichv is provided with anVr when the valve is closed under pressure: of la spring 119a is open. Line 106 connects with the solenoidfvalve unit of the casing 119 opens into a line 127k which leads to and connects with the valve 169, while in the same -vicinity` a line 136 leads from line 130 to drain, a relief valve 137 being incorporated therein. provided in the line 13) as shown. Ports 139 and 140 are provided in the wall. of the casing 68 which, when under the action of theisolenoid 1 11. Line 104 connectsV f vwith the solenoid valve unit at seating 115. A-portv117 electrical solenoid 120. The valve member 121 isprojL vid'edwith upper and lower conical Vparts 122fand123 at either end, the upper part closing Vonto a seating 124 and the lower part closing onto a seating 125 when ity at seating 124. A port 126 in the side'offthe upper partV Vthe valve 109. Lines 128 and 129 lead from the seat-Y the constant speed unit is in thek equilibrium position.

110 and-the lower half of which is provided with an'elec'- end, the upper part closing onto a seating 115 when the 147 ,of increased diameter.. Piston'143 is provided with a stem 148 extending to theright and incorporating conical parts 149 and 150, the maximum diameters of which are somewhat larger than the diameter of the central bore 146.V Part 149 is arranged to seat against the left-hand end Vof bore 146 when the piston 143 is moved yover to theyright whileV part l150 is arranged to seat against the l right-hand end of the bore 146 A'when the piston 143 is moved over to the left. A port 151 is provided in the casing-141 at its left-hand end to which the lineV 127 passes. A port 152-is provided at the right-hand end of -the'cas'ing to which the line 108 passes. A port 153 in4 the wall of the casing at the right-hand end of bore 142 receives line 1135,Y while a further port 154 is provided in the Wall of the central part of the valve and from this port the line 42, Le., the third oilway leads (as shown partly'in Figure l) to the propeller hub.

Referring now -to Figure 4 the electrical system associated with the propeller system comprises an electrical source (not shown) from which current passes through a lead 155 to either one of two circuits, the rstbeing operative when the aircraft is on the' ground and the second when the aircraft isin flight.

Taking the first circuit, a lead ,-156 is tapped from lead 155 and from it a lead 157 is taken to a stop withdrawal switch 158 arranged to be closed by the port main undercarriage oleo when the aircraft is on theY ground. 'AY

further lead -159 is taken to a pair of coils 160 and 161 arranged in parallel, which coils are respectively operl ably associated with'double-acting relay switches 162 and 163. From the coils 160 and 161 a lead 164 is taken through a stop withdrawal switch 165 which isV arranged to `begclos'e'd by the starboard.mainundercarriage oleo wall of the casing 80 through 'which'fluid pressure may i be applied to the undersideV ofthe stepped piston 90.` v

when the `aircraft is on the ground, to a lead 1 66 which connects with the negative side of the current source.' Lead 156 is taken to a contact 167 and the relay switch 1,62 is arranged when the aircraft yis on the ground andV i second contact( 168.: From contact 168 a lead 169 is A restriction 138 Vis i.e. during constant'speeding, are substantiallyA closed byf4 the lands 78 and 71 respectively. "From port 139 a line Y 31 is taken as shown partly in FigureV l to the propeller'V hub, while from port'140 a line 3-7 is alsotaken tothe propeller hub, lines 31 and 37 respectively constituting taken to a switch170 for each engine of the'power plant, these switches Ibeing closed at engine throttle settings at or near idlingA by suitable interconnection withthe engine throttles (not shown). A lead 171 is taken from lead,156 and connects with lead 169- before the throttle switch 17d. A switch172 arranged to be closed by the undercarriage nose wheel oleo when the aircraft is on the ground, is included in lead V171. A lead 173 is taken from switch 173 to a coil 174`constituting the winding of the solenoid 1,20 of the solenoid valve unit 107 (see Fig. 3) this solenoid lbeing, capable of initiating operation of the thirdoilway pitch stop retraction system. A lamp 175 is provided in the circuit to indicate when the coil 174 is energised. From this coil a lead 176 is taken to a contact 177 and the relay switch 163 is arranged, when the aircraft is on the groundand therefore the coil 161 is energised, to bridge this and a second contact 178. A lead 179 is taken from lead 176 and connects into a lead i1,80

talcenfrom Contact 17,8'. A switch 181 arranged to be vclosed by the undercarriage nose. wheel oleo"when the with `the negativeside ofthecurrent source.` A switch y 208 inthe lead i156 permits these' circuits to be opened in case of emergency. Y Y

- Tneleads 156, 171,173, 179 and180 comprise a lirst line across thesource of electric power 155, 166 and connects said source with the electromagnetic stop withdrawal means 174 through the stop i v Taking now the second circuit, it will be understood that when the aircraft is in flight switches 158 and 165 will vbe open so that coils 160 and 161 will not be energised, and thus the relay switches 162, 163 will not bridge contacts 167, 168 andv 177, i178. respectively. Instead they will bridge contacts i182; 183 and 184,185 respcc-'jV withdrawal switch means .172,

assetati tively. Nose wheel oleo switches 172 and 181 will also of course be open. A'lead 186 is taken from lead 155 to'one of the slip rings 56 (see also Fig. 1) shown diagrammatically as a contact in Figure 3. The second slip ring 57 is also shown as a Contact and thebrush 63 as a 5 bridge. This forms the switch shown generally as 55 in Fig. l. From slip ring S7 a lead 187 istaken to the lead 166 which connects with the negative side of the current source. A lead 188 is taken to lead 189 which connects contacts y132 and 185, while a lead 190 con- 10 nects contacts 183 and '184. A lead 191 is taken from lead 19d to a coil 192. Vwhich constitutes the winding 111 of the solenoid valve unit 105 (see Fig. 2) the solenoid capable of initiating'lifting of the constant speed unit valve 69 to effect coarsening of the pitch of the prol5 peller blades. A lead 193 is taken from this coil to the lead 156. The coil 192, the solenoid valve unit 105, the v line 113, the reduced portion 8i) and the port 80a of the casing 67 comprise electromagnetic overriding pitch coarsening means. A warning lamp 194 is included in 20 lead 187 to indicate when the switch SS is closed.

The leads 18st rough 191 and 193 comprise a second line across the source of electric power 155, 166 and connects said source with the electromagnetic overriding pitch coarsening means 192 through the propeller switch 25 means 51S.

The hydraulic and electric circuits hereinbefore described may also include feathering and de-icing circuits, engine-failure responsive means, safety valves and switches, and the like according to particular requirements, but these are not shown in order to simplify the description of the system.

The operation of the complete system will now be described with reference to Figs. l, 2, 3 and 4.

Under normal operating conditions pressure duid from the oil system of the engine driving the propeller is delivered through conduit 96 to the constant speed unit pump 97 and high pressure fluid therefrom isV delivered through the hydraulic line 99 and port 1% to the annular space between the lands 70 and '71 of the constant 40 speed unit valve 69. Under constant speeding conditions the valve is held in its equilibrium position so that ports 139 and 1d@ are substantially closed by the lands and thus only suiiicient fluid pressure is delivered to the pitch changing motor ram 15 to balance 4the centrifugal and aerodynamic moments on the blades. Should however the engine rpm. change, for example 4due to a change of aircraft trim or throttle opening, the governor iiyweights 7e will move inwardly or outwardly about their pivots 7 7 under the effect of centrifugal force, either lift- 50 ing the valve d against the coil spring S to eiect coarsening of the blades, iiuid pressure passing through port 13g, line 31, chamber 32, ports 35, annular chamber lid, ports 35, annular chamber 3o to the forward side of ram 15 to effect coarsening of the propeller blades, 55 or allowing it to move downwardly, fluid pressure passing through port lei-tl, line 37 ports 33 and 3%, annular chamber and ports l1 to the rearward side of ram 15 to eiect lining of the propeller blades. The speed setting of the propeller is varied by adjustment of the gear 35 and sliding cylindrical member which adjusts the loading of the coil spring 86. Y

High duid pressure is'conveyed through line to the solenoid valve unitlll, through line to tbe sole noid valve unit 1t?? and through line to the valve but no action occurs since the respective valvesl 113, e212' and 1563 are closed. n

When it is desired to override the constant speed unit to coarsen the propeller for purposes such as 'ill be described hereinafter, the solenoid 111 is energised valve 112, which is normally maintained so that conical part 113 is closed on to seating 115, will thon be moved so that conical'part 114 closes onto seating 116, seating 113 being opened and permitting high pressure fluid in line 104 to pass into the unit 195 and out through line 75 piston therefore compresses coil spring 93 and moves up,- wardly together withthe stepped cylindrical member 37 to which it is secured, taking up ,the lost'rnotion between the member 87 and the stern of the valve member 69. Shoulder 88 then'abuts againstpshoulder 7S and the valve 69 is consequently lifted against the effort of coil spring 86. Thus land 7) uncovers port 139 and the coarse pitch pressure line 31 is opened to the annular chamber between lands and 71, high pressure iluid passing therefrom to the forward side of the ram 15 to move the propeller blades towards coarse pitch.

When it is desired to adjust the pitch of the propeller to a ne pitch setting beyond the fine pitch stops 19 anV engine speed is selected which causes the propeller to tine ol until the chamfer 3u on the ring 29 is hard up against the line pitch, stop abutments 19. ln order to retract thene pitch stops the third oilway system is brought into operation by energising the solenoid 12d of the solenoid valve unit 167 valve 12,1 of which is normally maintained so that conical part 122 is closed onto seating 12d.Y Whensolenoid 121i is energised the valve 121 is moved so that conical part 123 closes onto seating 125. high pressure fluid in line 196 to pass into the unit `11)"1' and out through line 127 to the leftehand side of the piston in valve 1d?. The high pressure iiuid on the left-hand side of piston 143 overcomes the effort of coil spring 145 and the conical part 1459 on the stern 14S seats against the left-hand end of the bore 1+iwhile the conical part 15u, which normally seats against the right-hand end ofV this bore, moves away from its seat@ ing, thereby permitting high pressure iluid supplied to chamber 147 through line 16S to pass into bore 146 and out through port .1551i into the third oil line 42, through passages 13 and fait, annulus da', ports d and 47, annulus i3 and ports 49 to the forward side of the stop release piston 22. however until after the ram has corne up against the fine pitch stops. When this happens the pressure builds'k up on the forward side of the stop-release piston 22, and the lower fluid pressure on its opposite side, and the effort ofthe coil spring 26 are overcome so that the resultant pressure dierential causes the piston Z2, together with retaining ring 21, to move to the right. The abutments 19 therefore spring from the larger diameter 21a to the smaller diameter 2lb of the retaining ring 21, by virtue of the resilient fingers Ztl and the pressure of the ram 1S. Consequently the abutments 1i? are retracted sufliciently to permit the annular ring 29 to pass over them. Thus the ram 15 and annular ring 29 are free to move forwardly until the sleeve 27 contacts the abutnients 11i. to a superiine pitch to which the propeller is moved, for example, for the engine starting cycle to reduce the drag of the propeller and thereby enable faster cranking speeds and consequently better starting to be obtained.

Superne pitch may also be used during landing, when the aircraft has touched down to produce aerodynamic braking by-the blades.

Fluid pressure from the conduit @d (i.e. engine oil pressure) passes through line 13d, Vchamber 74 and bore "12 into the governor flyweight chamber of the constant speed unit and back through port 131 into 139 'and passes through restrictor 133 across which the pressure drops to a suitably low value determined by the relief valve From this point it passes to'lines 128 and 129 leading to the Solenoid valve units 1&5 and 1d? respectively. When these units are closed to high pressure fluid from the constant speed unit, this low presrEhus seating 124- is opened and permitsv The stop release piston is not moved This position of the ram 15 correspondsV this low pressure fluid tothe right-hand side of piston 143 and also through .port Y154 into the third oil line.y 42.

so far described operates inl-known essere@ e vthe plunger, coil spring 5411, sliding member 62 and brush 63 all moving to the right together until the .brush contacts the slip rings r56. and 57. Further depression of theplunger is taken upby the c'oil'spring 54b thereby applying further pressure on the brush and also rpermitting the cam to move over the cam lever. The cam 51, cam lever 52, brush 63 and slip'rings 56 and 57 thus constitute means for detecting when the propeller has fined off to a predetermined pitch setting iiner than normally set by Vsaid fine pitch stop.

The system is such that when the aircraft is on the ground and superi-lne pitch is selected for. starting or any other purpose the switch 55 is isolated so that it does not intiate coarsening of the propeller blades, the blades moving normally into superine pitch. Should however the ne pitch stop abutments fail in their retracted po sition during ight any movement of the propeller blades more than twoV degrees below the normal ne pitch angle causes closing of the switch 55 and through the electrical circuit shown in Fig. 3 initiates, as hereinafter described temporary coarsening of the blades toprevent ahigh propeller drag from developing by the propeller. Y

constant-speeding down to super-fine pitch.

vilssuming the aircraft has touched down on landing then Vthe o leo switches S, 165,172 and 181Lare closed*- that mally1no danger Aof this occurring' during tale-G be Such movegerous results.

Thus according to this invention as soon as the aircraft leaves the ground the oleo switches 158, 165, 172 and 181 are vopened so thatthe coils 160l and 161 are deenergised. Consequently' relay switches 162 and 163. move from contacts 167, 168 and 177, 178 to bridgek contacts 182, 183 and 184, 185, thereby isolating the on-ground circuit and bringing the flight circuit into operation. The oleo switches 158 and 165 constitute a means for detecting tlight conditions in which the abutments 19 limit the movement of the ram 15 in the pitch ining direction. Thisv circuit includes the switch 55 and coil 192` for operating the solenoid valve unit 105. If a during iiight the abutments 19 remain in the retracted position and the ram 15 and propeller blades move below the tine pitch setting by for example two degrees, the switch 55 is automatically closed. This immediately completes the circuit formed by leads 155, 186, 187, 188,` 189, 190, 191, 193 and 166 thereby energising coil 192 and also illuminating the lamp 194. Consequently the solenoid valve permits high pressure oil to pass through line 118to the underside of piston 90 which lifts the constant speed unit valve 69. This, as previously described, permits high pressure uid to pass to the forward side of the ram'15 to coarsen the pitch of the propeller blades.

It-will be Vunderstood that the above sethe intermittent flashing Yof the lamp 194 will warn the Assuming also that the engine throttle i's.clo'scd.ornearly u closedie. Aat ground idling or flight idling .position then` theswitch 170 Ais closed. Since' switches'158and 165" y are closed ythe coils' 160 and 161'a're energised and the -relay switches 162 and 163 bridge contacts 167, 168 and 177, 178 respectively. Thus the circuit including leads 155, 156, 169, 171, 173, coil 17'4 and leads 176, 179,- 180 and 166 is completed and the indicator lamp 175V lights up. Consequently solenoid valvek unit 107 is operated to convey high pressure uid from line 106 through line 127 towards the valve 109. This high pressure uid passes into the valve from line 127 through port 151 to the left-hand side of piston 143 thereby moving this piston to the right against the coil spring 145 whereupon the conical part 150 is unseated and conical part 149 seated so that the high pressure Yiiuid inline 108 and bore `1474 is permitted to pass into the third oilway 42 via port 154. This effects retraction of the abutments;

19 as already described, because the propeller will have constant speed toward fine pitch and the ram will have been brought up against the fine pitch 'stops to allow sufficient pressure to build up in theV third oilway to move the stop release piston 22. i Y

In the flight setting position of throttle, the constant speed unit governor is set to select an rpm. greater than can be achieved by the engine with the fuel supply at the flight idling setting'of the throttle. When throttled back therefore the constant speedJunit selects pitch ning whichrbrings the Yrain hard againstthe fine pitch stops so that a pressure differential is developed in the third oilway suti'icient to'break down the tine, pitch stops.

Y one fails to close on-landing the Hight circuit is still providing both relays 162 and16-3- Vit may happen however that Vthe'abutments 19 remain jammed in their retracted position `due to seizure of the piston 22, fracture of the coil spring 26 or other failure. Such failure may occur just prior to flight when the aircraft is on the ground and if no safety arrangements were provided the propeller blades might move to a 'superiine pitch in ight e.g. when the engine is throttled back after take-oit or before touch down (there is norisolated by the other propellerlpitch above the Vpitch at which the; switch 55 the aircraft is on the ground with the engine throttle wide open, both ground and ilight electrical circuits are inoperative, this also .being so when the nose Wheel 1 leaves the ground. As soon as the main wheels leave the ground however, the flight 4circuit' becomes operative irrespective of throttle setting.

.If lthe fine pitch `stop abutments fail in the retracted position prior to landing of the aircraft and if the blades. move to a sutliciently tine pitch the switch 55 is closed and initiates temporary coarscning of the propeller blades; to prevent high drag. As soon as the main wheels of the undercarriage touch down the oleo switches 158 and 165 'are closed and operate relays 160 and 161 to bring the ground circuit into operation and isolate'the flight circuit. Then, with the throttle set at idling r.p.m.. or flight idling rpm., the blades can -rnove into the superiinerpitch position toproduce aerodynamic braking., When f'. the Inose wheel touches down the switches 172 andv 181. close, and in the event of either one ofthe relays 162 andl 163 failing tooperate to close the ground circuit contacts 167,168 or 177, 178 permit energising of the coil 174.

Two main wheel voleo vswitches are provided .since if one fails to open'during take-offY the other still isolatesV the groundfcircuit f- Two nose `wheeloleo switches are provided since if operate normally.

The switches isz, 183,162; ist, iss, 16s compriset primary or first detecting switch means operatively-con nected to the primary detecting'me'ans, comprising switches 158, and 165-, for detecting conditions under which the pitch ning movement of the propeller should be limited.

by the' stop means :19, 21, 22, the primary detecting. 4

This coarsening is temporary since as 'soon as Y switch55 is opened by movement of the blades the valveV Y 69 is released. 35 Yquencefwill reoccureach time switch 55 is closed but it Y switches 182, 183; 184, 185 being closed when the primary'pdetecting means detects the said conditions.

The switches 162, 1a?, 163; 163, 177, `i78 compriseV second detecting switch means operativelyv connected to the primary detecting means, comprising switches 158 and 165', the second detecting switches 167, 168; 177, 17:5 being'opened when said primary detecting means detects conditions under which the pitch `fining movements of the propeiler should be limited by the stop means 19, 21, 22 and closed when tl e primary detecting means detects other conditions.

We claim:

l. A variable pitch propeller for an aircraft comprising pitch iining means for iining the pitch of the propeller; pitch coarsening means for coarsening the pitch of the propeller; stop means limiting the tining movement of the propeller; electromagnetic stop withdrawal means connected to said stop means and operable to render the stop means inoperative; stop withdrawal switch means adapted to be closed when the undercarriage of the aircraft is on the ground; propeller switch means in eiective operative connection during flight of the aircraft with said propeller to be closed by said propeller when it lines ofi to predetermined amount iiner than that set by the stop means; electromagnetic overriding pitch coarsening means connected to said pitch coarseningy meansy and operable to initiate pitch coarsening movement `of said propeller; and an electric circuit comprising a source of electric power; a iirst line across said source and connecting said source with said electromagnetic stop withdrawal means through said stop withdrawal switch means; and a second line across said source and' connecting said source with said electromagnetic overriding pitch coarsening means through said `propeller switch means.

Y2. A variable pitch propeller for an aircraft comprising pitch yiining means for fining the pitch of the propeller; pitch coarsening means for coarsening the pitchk of the propeller; stop means limiting the fining movement of the propeller; electromagnetic stop withdrawal means connected to the stop means and operable to render the stop means inoperative; a double-acting switch arrangement comprising two switches connected so that when one is open the other is closed and viceversa, one of which is adapted to be closed when the undercarriage of the aircraft is on the ground; propeller switch'means in effective operative connection during flight of the aircraft with said propeller to be closed by said propeller when it fines oif to predetermined amount finer than that set by the stop means; electromagnetic overriding pitch coarsening means connected to said pitch coarsening means and operable to initiate pitch coarsening movement of said propeller; and an electric circuit comprising a source of electric power, a iirst line across said source and connecting said source with said electromagnetic stop withdrawal means through one of said two switches and a second line across said sourceand connecting said source with said electromagnetic overriding pitch coarsening means through said propeller switch means and the other of said two switches.

3. A variable pitch propeller for an aircraft comprising pitch iining means for iining the pitch of the propeller; pitch coarsening means for coarsening the pitch of the propeller; stop means limiting the fining movement of the propeller; electromagnetic stop withdrawal means connected to said stop means and operable to render the4 stop means inoperative; stop withdrawal switch means adapted to be closed when the undercarriage of the aircraft is on the ground; a double-acting switch arrangement comprising two switchcs connected so that when one is open the other is closed and vice versa; propeller switch means in effective operative connection during iiight of the aircraft with said propeller to be closed by said propeller when it nes off to predetermined amount finer than that set by the stop means;

a first line across said source and connecting said source with said'electromagnetic stop withdrawal means through said stop withdrawal switch means and one of said two switches which latter is in parallel with said stop withdrawal switch means; and a second line across said source connecting said electromagnetic overriding means with said source through said propeller switch means and the other of said two switches.

4. A variable pitch propeller for an aircraft which propeller comprises pitch coarsening means for coarsenf.`

be limited by the stop means; said first detecting switchV means being closed when said primary detecting means. detects the said conditions; propeller detecting means operatively connected to the propeller to detect when the propeller has iined oi further than the amount set by said stop means; propeller switch means during Hight of the aircraft being effectively operatively connected toV said propeller detecting means to be closed thereby when said propeller detecting means detects that the propeller has iined off further than the amount set by said stop means; electromagnetic overriding pitch coarsening means operatively connected to initiate coarsening movement of said propeller; an electric circuit comprising 4a 'source of electrical power; a first line `across said source and incorporating in series said first detecting switch meansand said electromagnetic stop withdrawal means whereby the latter isenergized whenever said iirst detecting switch means is closed, a second line in parallel with said rst line across said source and incorporating in series said propeller switch means and said elect-romagnetic overriding pitch coarsening means whereby the latter is energized Iwhenever said propeller switch means is closed, and stop withdrawal signal means operatively connected in said iirst line in series with said rst detecting switch means and in parallel with said electromagnetic stop withdrawal means to emit a signal when said stop withdrawal means is operative.

5. A variable pitch propeller for an aircraft which propeller comprises pitch coarsening means for coarsening the propeller pitch, pitch iining means for ning oft the propeller pitch; stop means for limiting the -ning movement of the propeller; electromagnetic stop withdrawal means operatively connected to said stop means, Iand operable to render the latter inoperative; primary detecting means including a first detecting switch means adapted to be closed when the undercarriage of the air- Y craft is on the ground for detecting conditions under which the pitch ning movement of the propeller should be limited by the stop means; said iirst detecting switch means being closed when said primary detecting means detects the said conditions; second detecting switch means operatively connected to said primary detecting means to be opened when said primary detecting means detects said conditions and closed when said primary detecting meausdetects conditions other than said conditions; propeller detecting means operatively connected to the propeller to detect when the propeller has fined oit further thanV the amount set by the said stop means; propeller switch means during flight of the aircraft being effectively operatively connected to said propeller detecting means detects that the propeller has fined oli further than the` amount set by said stop means; electromagnetic over-y riding pitch coarsening means operatively connected to initiate coarsening movement of said propeller; and an electric circuit comprising a source of electrical power; a rst line across said source and incorporating in series said rst detecting switch means and said electromagnetic stop withdrawal means whereby the latter is energized whenever said first detecting switch means is closed; and 4a second line in parallel with said rst line 'across said source and incorporating in series said propeller switch means, said second detecting switchmeans, and said electromagnetic overriding pitch coarsening means whereby the latter is energized whenever both said propeller switch Imeans and said second detecting` switch means are closed( n f6; The Variable pitch propeller of claim 5 further comprising a propeller switch signal means operatively connected in said second line in series with lsaid propeller Aswitch means and in parallel -with said second detecting operative,primary detecting means for detecting conditions under which the pitch iining movement of the propeller should be limited by the stop means including the undercarriage and rst detecting switch means operat detects said conditions., propeller detecting means operatively connected to the nndercarriage tobe opened thereby, during flight only, when said primary detecting means tively connected to the propeller to detect when the propeller has iined oi further than the amount set by said stop, means, propeller switch means operatively connected to said propeller detecting means to be closed thereby when said propeller detecting means detects that the pro-V peller has fined off further than the `amount set by said stop means, electromagnetic overriding pitch coarsening means operatively connected. to the propeller `pitch coarsening means to initiate coarsening movement ofA said propeller, said Vconnection between the y undercarriage and said rst 'detecting switch means causing said first detecting switch means to close when the nndercarriage contacts the ground, and an electric circuit comprising a source of electrical power, a rst line aci-oss said source and connecting said electromagnetic stop withf drawal means to said source throughrsaid first detecting switch means when said rst detectingswitch meansl is closed to energize said electromagnetic stop withdrawal lmeans, and a second line across-said source connecting said source to said electromagnetic overriding pitch coarsening means through said propeller switch means to energize the said electromagnetic overriding pitch coarsening means when said propeller switch means is closed.

References Cited in the tile of this patent UNITED STATES PATENTS l v2,593,910 Morris'et al. Apr. 22, 1952 2,600,017y Morris et al. .Tu-ne 10, *"1952 2,652,122 Longfellow Sept. 15, 1953 2,655,999 Basevi Oct. 20, 1953 2,663,373 Richmond Dec.` 22, 1953 2,699,304 Treseder et al. Jan. 1l, 1955 

